Project Summary Problems with anger and aggression are typical after a moderate to severe traumatic brain injury (TBI). However, the need for effective treatments for these problems in the TBI population remains unmet and presents a major rehabilitation challenge and public health need. This is a public health concern due to the vast array of negative consequences associated with anger and aggression problems, including interpersonal difficulties, caregiver burden, social isolation, violent criminal offenses, reduced community re-integration, and poorer health and overall well being. Recent research suggests that anger and aggression after TBI are associated with distorted interpretations of others? actions; assuming people?s actions are more hostile than they truly are (hostility bias). Observed in 37% of participants with moderate to severe TBI, hostility bias is a common problem contributing to post-TBI anger and aggression that must be addressed. In response to this issue, a novel treatment, Intervention to Change Attributions that are Negative (ICAN), was created. This treatment aims to modify hostile attributions as an anger management approach for people with a TBI. ICAN incorporates a unique perspective taking technique to encourage more benign interpretations of others? actions. Reductions in hostile attributions are expected to result in decreased anger and aggression. ICAN is a six-session group therapy treatment, delivered once a week for six weeks. A Phase I, randomized waitlist controlled trial will be conducted in 40 adult participants with moderate to severe TBI who have hostility bias and are at least one-year post-injury. There will be three data collection points: Baseline; Posttest I; and Posttest II. Study aims are to examine feasibility and satisfaction, and effect sizes of the ICAN treatment on perspective taking, hostile attributions about others? behaviors, anger, and aggression. The long-term goal is to provide a novel intervention that addresses the clinical need for effective treatments of anger and aggression after TBI. If current study objectives are met, it advances the goals of expanding evidence-based treatments for anger and aggression post-TBI. Researchers and clinicians may see the benefits of targeting hostile attributions and using a perspective-positioning approach for treating anger and aggression, increasing likelihood of adoption. ICAN adoption into standard anger management has the potential to substantially change clinical practice and enhance rehabilitation outcomes, psychosocial functioning, and community integration after TBI.